Tightening device and tightening method

ABSTRACT

A tightening device and a tightening method are able to check that a fastening member has been fastened to a desired set torque or greater after being tightened, without loosening the fastening member. The tightening device executes a first tightening process of adjusting the output of a motor after measured torque that is measured by a torque detector has reached a preset first control start torque, such that the measured torque reaches a preset first set torque in a phased manner through repeated increases and decreases in torque, and blocking power supply to the motor when the measured torque reaches the first set torque, and then executes a second tightening process of driving the motor at an initial output that is less than in the first tightening process, adjusting the output of the motor after the measured torque that is measured by the torque detector has reached a preset second control start torque, such that the measured torque reaches a preset second set torque in a phased manner through repeated increases and decreases in torque, and blocking power supply to the motor when the measured torque reaches the second set torque.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a tightening device and a tighteningmethod that are able to confirm that a fastening member such as a boltor a nut is tightened to a set torque or greater.

2. Description of the Related Art

In order to increase the accuracy with which fastening members such asbolts or nuts are tightened, a known tightener measures the tighteningtorque that acts on the fastening member, and is numerically controlledto end the tightening when the measured torque reaches a set torque(e.g., see JP 2013-166211A).

Also, additional tightening that involves torque being further appliedto tighten a fastening member that has already been tightened isperformed in some cases (see JP 2013-166211A).

There is a need for a way of checking whether tightening has actuallybeen performed to a desired set torque or greater, after a fasteningmember has been tightened or after additional tightening has beenperformed.

In tightening the wheel nuts of a vehicle, the wheel nuts are firstlytightened and run in, and then loosened and tightened again in order tocheck whether tightening has been performed to a prescribed set torque.Further running in thus needs to be performed when wheel nuts that havealready been tightened once are loosened and retightened, making itdifficult to determine whether the tightening torque has really reachedthe set torque.

An object of the present invention is to provide a tightening device anda tightening method that are able to check that a fastening member hasbeen fastened to a desired set torque or greater after being tightened,without loosening the fastening member.

SUMMARY OF THE INVENTION

In order to solve the above problems, a tightening device of the presentinvention is a tightening device including a motor, a motor drivecircuit that drives the motor, a drive shaft that is rotated by themotor, has a socket mounted on a tip thereof, and is configured totighten a fastening member, a torque detector that detects a tighteningtorque that acts on the socket, and a control unit that controls themotor drive circuit based on a set torque set in advance and a measuredtorque measured by the torque detector. The control unit executes afirst tightening process of controlling the motor drive circuit,adjusting an output of the motor after the measured torque that ismeasured by the torque detector has reached a preset first control starttorque, such that the measured torque reaches a preset first set torquein a phased manner through repeated increases and decreases in torque,and blocking power supply to the motor when the measured torque reachesthe first set torque, and then executes a second tightening process ofcontrolling the motor drive circuit to drive the motor at an initialoutput that is less than in the first tightening process, adjusting theoutput of the motor after the measured torque that is measured by thetorque detector has reached a preset second control start torque, suchthat the measured torque reaches a preset second set torque in a phasedmanner through repeated increases and decreases in torque, and blockingpower supply to the motor when the measured torque reaches the secondset torque.

Also, a method of controlling a tightening device according to thepresent invention is a method of controlling a tightening device thatincludes a motor, a motor drive circuit that drives the motor, a driveshaft that is rotated by the motor, has a socket mounted on a tipthereof, and is configured to tighten a fastening member, and a torquedetector that detects a tightening torque that acts on the socket. Themethod includes a first tightening process of controlling the motordrive circuit, adjusting an output of the motor after the measuredtorque that is measured by the torque detector has reached a presetfirst control start torque, such that the measured torque reaches apreset first set torque in a phased manner through repeated increasesand decreases in torque, and blocking power supply to the motor when themeasured torque reaches the first set torque, and a second tighteningprocess of controlling the motor drive circuit to drive the motor at aninitial output that is less than in the first tightening process,adjusting the output of the motor after the measured torque that ismeasured by the torque detector has reached a preset second controlstart torque, such that the measured torque reaches a preset second settorque in a phased manner through repeated increases and decreases intorque, and blocking power supply to the motor when the measured torquereaches the second set torque.

Effects of the Invention

According to the tightening device and the tightening method of thepresent invention, a fastening member is tightened with a first settorque as a target value in a first tightening process, and then, in asecond tightening process, a motor is driven at an initial output thatis less than the initial output in the first tightening process, andtightening is implemented with a second set torque as the target value.By performing this second tightening process, it can be confirmed thatthe fastening member is tightened to at least the second set torque.

The second tightening process is able to prevent over-tightening, orso-called overshooting, with respect to the second set torque, since theinitial output of the motor is less than in the first tighteningprocess, and tightening is performed by increasing the torque in aphased manner through repeated increases and decreases in torque.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a tightening device accordingto one embodiment of the present invention.

FIG. 2 is a block diagram of a tightening device according to oneembodiment of the present invention.

FIG. 3 is a flowchart showing the overall flow of a tightening methodaccording to one embodiment of the present invention.

FIG. 4 is a flowchart showing a mode switching flow of a tighteningdevice according to one embodiment of the present invention.

FIG. 5 is a flowchart showing a set torque changing flow of a tighteningdevice according to one embodiment of the present invention.

FIG. 6 is a flowchart showing a tightening flow of a tightening deviceaccording to one embodiment of the present invention.

FIG. 7 is a graph showing the change in tightening torque in a normaltightening mode of a first tightening process, and a graph showing thechange in motor output.

FIG. 8 is a graph showing the change in tightening torque in a hardtightening mode of a first tightening process, and a graph showing thechange in motor output.

FIG. 9 is a graph showing the change in tightening torque in a checkingtightening mode of a second tightening process, and a graph showing thechange in motor output.

FIG. 10 shows the table showing the results of a working example 1.

FIG. 11 shows the table showing the results of a working example 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment in which a tightening device 10 of thepresent invention is applied to a numerically controlled tighteningdevice constituted by a tightener 20 serving as a main body thatperforms the tightening, a control device 30 that controls the tightener20, and a torque detector 50 that measures torque, as shown in FIGS. 1and 2, will be described. Note that a configuration can also be adoptedin which some or all of the functions of the control device 30 areincorporated in the tightener 20, or some of the functions of thecontrol device 30 may be executed by an external PC or the like.

Also, in the following embodiment, the tightening process consists of afirst tightening process and a second tightening process as shown inFIG. 3, with the first tightening process including a normal tighteningmode and a hard tightening mode that depend on the member beingfastened, and the second tightening process serving as a checkingtightening mode that can check whether the tightening torque is a settorque or greater.

FIG. 1 is a diagram illustrating an outline of the tightening device 10of the present invention, and FIG. 2 is a schematic block diagram of thetightening device 10. As shown in the diagrams, the tightening device 10is constituted by the tightener 20 and the control device 30, and thetightener 20 is provided with the torque detector 50 which detectstorque acting on a socket.

Tightener 20

In the embodiment shown in FIG. 1, a double-shaft power wrench in whicha drive shaft 21 consists of an inner shaft and an outer shaft 22 isexemplified as the tightener 20. However, the power wrench is notlimited to a double-shaft power wrench and may be a single-shaft powerwrench, and the tightener 20 may be an impact wrench, an impact driver,an impact/hammer drill, or the like.

With the double-shaft tightener 20, the inner shaft and the outer shaft22 forming the drive shaft 21 can be rotated in opposite directions toeach other by a motor 24 built into a housing 23. The inner shaft andthe outer shaft 22 can be connected to the motor 24 by a decelerationmechanism 28 such as a planetary gear mechanism.

The tightener 20 is provided, at a tip of the inner shaft, with a socketthat is capable of mounting a fastening member such as a bolt or a nut.Also, a reaction receiver 25 that is equipped with an arm whose tipprojects in a substantially perpendicular direction relative to theaxial center of the drive shaft 21 is attached to a tip of the outershaft 22.

The tightener 20, on receiving an instruction from a control device 30shown in FIG. 2 as a result of a trigger switch 26 shown in FIG. 1 beingoperated, drives the motor 24 and rotates the drive shaft 21. Also, asshown in FIG. 1, the tightener 20 is equipped with a switch 27 forforward-reverse switching, and the rotation of the motor 24 can bereversed by operating the switch 27 for forward-reverse switching toenable tightening and loosening of a fastening member. The switch 27 forforward-reverse switching can be given as a switch that switches therotation of the drive shaft 21 between forward and reversemechanistically, through a gear change, clutch operation or the like ofthe deceleration mechanism 28. Also, the switch 27 for forward-reverseswitching may be a switch that reverses the voltage that is supplied tothe motor 24.

Torque Detector 50

The tightener 20 is equipped with the torque detector 50 for detectingthe torque acting on the socket. The torque detector 50 transmits asignal relating to torque to the control device 30. As shown in FIG. 1,a torque detector in which a torque sensor 51 that detects tighteningtorque is directly mounted between the drive shaft 21 and the socket canbe employed as the torque detector 50. The torque acting on the socketmay be torque detected from a change in the electrical system of thetightener 20, such as the change in motor current, for example. Also,the torque acting on the socket may also be obtained through conversionfrom the rotation angle of the drive shaft 21, the motor 24, thedeceleration mechanism 28 or the like.

Because the torque detector 50 rotates in tandem with the drive shaft 21when mounted in the drive shaft 21 as shown in FIG. 1, cable connectionwith the control device 30 is not possible. Accordingly, it is desirablethat the signal relating to tightening torque measured by the torquesensor 51 is amplified by an amplifier circuit 52, input to the CPU 54after undergoing A/D conversion in an A/D converter circuit 53, andwirelessly transmitted via a RF (Radio Frequency) circuit 55 and anantenna 56, as shown in FIG. 2. Power supply to the torque detector 50can be performed by installing a small battery in the torque detector50.

As a specific embodiment, a distortion gauge adhered to the outer shaft22 can be exemplified as the torque sensor 51. The tightening torqueacting on the outer shaft 22 is output as a voltage change caused by theresistance change of the distortion gauge.

Control Device 30

The control device 30 is, as shown in FIG. 1, electrically connected tothe tightener 20 by a connection cable 60, and is capable ofcommunicating with the tightener 20 and supplying power to the tightener20. Also, the control device 30 can be connected to a commercial powersource by a power cable 62 that has a plug 61 connected to a tipthereof. Note that a configuration can also be adopted in which thecontrol device 30 and/or the tightener 20 are battery operated, thecable 60 for connecting the control device 30 and the tightener 20 isomitted, and the control device 30 and the tightener 20 perform wirelesscommunication.

As a specific embodiment, the control device 30 incorporates a controlmeans 32 shown in FIG. 2 in a box-type casing 31, as shown in FIG. 1.The control means 32 is provided with a control unit 33 that is mainlyconstituted by electronic components including a CPU 34, a memory 35such as RAM or ROM, and a D/A converter, and can be realized by variousprograms or the like stored in the memory 35. In FIG. 2, a functionalblock relating to typical functions that are realized by theseconnections is depicted. It should naturally be understood that thesefunctional blocks can be realized using only hardware, only software, ora combination of hardware and software.

A set torque display unit 40 that displays a set torque that is desiredby a user, and a measured torque display unit 41 that displays thetightening torque measured by the torque detector 50 are provided on onesurface of the casing 31, as shown in FIG. 1. Also, torque settingbuttons 47 and 48 for the user to increase or decrease the set torque,and a mode switching switch 44 for switching between a normal tighteningmode and a hard tightening mode that serve as a first tightening processand a checking tightening mode that serves as a second tighteningprocess are provided. Furthermore, a torque setting range display unit46 that indicates the range over which the set torque of the tighteningdevice 10 can be set is provided on the casing 31.

A digital display employing LEDs, for example, can be used for the settorque display unit 40 and the measured torque display unit 41. One orboth of these display units can, in the case where an anomaly of somekind occurs in the tightening device 10, be used as an error displayunit for displaying the anomaly. Note that, in FIG. 1, reference numeral42 denotes a set torque sub display unit that displays the set torquewhen the torque setting buttons 47 and 48 are operated, and is smallerthan the set torque display unit 40.

The torque setting buttons 47 and 48 are a minus button 47 for reducingthe set torque and a plus button 48 for increasing the set torque. Thesetorque setting buttons 47 and 48 can also be used as error cancellationbuttons by operating one of the buttons when an anomaly of some kindoccurs in the tightening device 10.

The mode switching switch 44 is a switch for switching the tighteningmode between the first tightening process and the second tighteningprocess, and a dial switch, for example, can be employed therefor. Thetext “Normal”, “Hard” and “Checking” are marked on the casing 31 atcorresponding positions, so as to enable the user to see what tighteningmode the mode switching switch 44 is set to. The mode switching switch44 may obviously be a button switch or a slide switch.

The torque setting range display unit 46 indicates the minimum andmaximum set torque of the tightening device 10, as shown in FIG. 1. Thesetting range stamped into a plate as shown in FIG. 1 or printed on asticker and attached to the casing 31 can be exemplified as the torquesetting range display unit 46. A digital display can also be usedtherefor similarly to the above set torque display unit 40 and the like.

The control unit 33 constituting the control means 32 has, as shown inFIG. 2, the abovementioned display units 40, 41 and 42, buttons 47 and78, and mode switching switch 44 connected thereto, together with amotor drive circuit 36 for driving the motor 24 of the tightener 20 viathe trigger switch 26, and an RF circuit 37 and an antenna 38 forperforming wireless communication with the torque detector 50. Forexample, output adjustment of the motor 24 by the motor drive circuit 36can be performed by phase control or PWM control.

All programs for controlling the tightener 20 are stored in the memory35. For example, stored in the memory 35 are set torques set by the userin correspondence with the respective tightening modes of the firsttightening process and the second tightening process, tighteningprograms and various parameters corresponding to the respectivetightening modes, the residing tightening mode, the control amount ofthe motor drive circuit 36 for adjusting the output of the motor 24based on the measured torque that is received and the set torque, andthe like.

Control of the tightening device 10 configured such as described abovecan be broadly divided, as shown in FIG. 3, into a mode switching flow(FIG. 4, step S001), a set torque changing flow (FIG. 5, step S002), anda tightening flow (FIG. 6) including the first tightening process (stepS003) and the second tightening process (step S004).

Mode Switching Flow

The mode switching flow is a flow for switching between the firsttightening process and the second tightening process, which in thepresent embodiment involves switching between the normal tightening modeand the hard tightening mode of the first tightening process and thechecking tightening mode of the second tightening process.

More specifically, as shown in FIG. 4, this involves processing forswitching, when the mode switching switch 44 is operated (step S101),the residing tightening mode between the normal tightening mode and thehard tightening mode of the first tightening process and the checkingtightening mode of the second tightening process (step S102), andstoring the residing tightening mode in the memory 35 of the controlunit 33 (step S103). Note that, in order to prevent erroneous operation,it is desirable to deactivate operation of the mode switching switch 44during the set torque changing flow, the first tightening process, andthe second tightening process which will be discussed later.

Set Torque Changing Flow

The set torque changing flow (step S002) shown in FIG. 5 is performedafter the mode switching flow (step S001) as shown in FIG. 3. This settorque changing flow is executed following the mode switching flow atthe time of the initial setting of the tightening device 10 or in thecase of changing the set torque of the respective tightening modes. Inthe present embodiment, the set torque (first set torque) of the normaltightening mode, the set torque (first set torque) of the hardtightening mode, and the set torque (second set torque) of the checkingtightening mode are set. In the case of using the tightening device 10in a state where the set torque has already been set or changed,execution of the set torque changing flow can be skipped.

The set torque changing flow is for setting and storing the set torquefor the residing tightening mode, when the torque setting buttons 47 and78 are operated.

As a specific embodiment, when the torque setting button 47 or 48 isoperated (step S201), the control unit 33 increments or decrements theset torque that is stored in the memory 35 by the designated value,according to the operation of the torque setting button 47 or 48 (stepS202), as shown in FIG. 5. Processing for storing the new set torque inthe memory 35 as the set torque is then performed (step S203).

Note that it is desirable to deactivate operation of the torque settingbuttons 47 and 48 during the mode switching flow, the first tighteningprocess and the second tightening process in order to prevent erroneousoperation, and a configuration may also be adopted in which theprocessing moves to step S203 after waiting for the torque settingbutton 47 or 48 to subsequently be operated within a predetermined timeperiod after the torque setting button 47 or 48 has been operated.

Tightening Process

After the set torque of each tightening mode has been set using the settorque changing flow (step S002), actual tightening process that dependson the selected tightening mode (step S003, step S004) follows, as shownin FIGS. 3 and 6.

Description of Tightening Modes

Here, an outline of each of the tightening modes consisting of thenormal tightening mode and the hard tightening mode of the firsttightening process, and the checking tightening mode of the secondtightening process according to one embodiment of the present inventionwill be described.

Although the values differ, in each tightening mode, as shown in FIGS. 7to 9, the motor 24 is started at a predetermined initial output (V0) andmaintains the initial output (V0). After the measured torque that isdetected by the torque detector 50 has reached a predetermined controlstart torque (VF) (the first control start torque in the firsttightening process, and the second control start torque in the secondtightening process), the output of the motor 24 is feedback controlledbased on the measured torque. In feedback control, the motor 24 isdriven while adjusting the output within a predetermined range definedby a maximum output (VR) and a minimum output (VB) of the motor 24. Themeasured torque thereby increases in a phased manner through repeatedincreases and decreases in torque.

Power supply to the motor is then blocked when the measured torquereaches the set torque set in advance.

Normal Tightening Mode (First Tightening Process)

The normal tightening mode is a tightening mode in which the motor 24has a large initial output, and is a tightening mode suitable fortightening a fastening target with respect to which the torque incrementfrom 10% to 100% of the target torque is equivalent to an angulardisplacement of over 27 degrees (ISO 5393).

In the normal tightening mode, the initial output (V0) of the motor 24,as shown in FIG. 7, is the largest of the three tightening modes (seeFIGS. 7 to 9). Accordingly, there is a risk of the tightening torqueovershooting if this normal tightening mode is used to tighten afastening target with respect to which the torque increment from 10% to100% of the target torque is equivalent to an angular displacement of 27degrees or less. On the other hand, because the motor 24 has a largeinitial output, there is an advantage in that tightening can beperformed in a short time.

Hard Tightening Mode (First Tightening Process)

The hard tightening mode is a tightening mode suitable for tightening afastening target with respect to which the torque increment from 10% to100% of the target torque is equivalent to an angular displacement of 27degrees or less (ISO 5393).

The hard tightening mode is a tightening mode in which the initialoutput (V0) of the motor 24, as shown in FIG. 8, is less than or equalto the normal tightening mode, and greater than the checking tighteningmode discussed below. Thus, although overshooting of the tighteningtorque can be prevented, tightening will take longer than the normaltightening mode.

Checking Tightening Mode (Second Tightening Process)

The checking tightening mode is a tightening mode for checking, afterthe normal tightening mode or the hard tightening mode of the firsttightening process, whether a fastening member tightened in either ofthese tightening modes is tightened to a predetermined torque orgreater.

The checking tightening mode is a tightening mode in which the initialoutput (V0) of the motor 24, as shown in FIG. 9, is less than in thenormal tightening mode and the hard tightening mode.

Thus, although the checking tightening mode takes longer to reach thepredetermined set torque due to the low initial output (V0) of the motor24 that is set, there is an advantage in that over-tightening(overshooting) can be prevented.

A more detailed control flow in the tightening modes is shown in FIG. 6.Note that although the first tightening process and the secondtightening process are described together, when tightening a fasteningmember, first, the first tightening process of step S003 (normaltightening mode or hard tightening mode) is executed, and then thesecond tightening process of step S004 (checking tightening mode) isexecuted after tightening the fastening member to a predetermined settorque.

Selection of the normal tightening mode and the hard tightening mode inthe first tightening process can be performed such that the normaltightening mode is selected in the case of a fastening target withrespect to which the torque increment from 10% to 100% of the targettorque is equivalent to an angular displacement of over 27 degrees, andthe hard tightening mode is selected in the case of a fastening targetwith respect to which the torque increment from 10% to 100% of thetarget torque is equivalent to an angular displacement of 27 degrees orless.

The tightening flow is started by turning on the trigger switch 26 in astate where the socket of the tightener 20 is fitted to the fasteningmember (step S301). With the tightener 20 shown in FIG. 1, the triggerswitch 26 is turned on by the user pulling the trigger switch 26 with afinger.

When the trigger switch 26 is turned on (step S301), the control unit 33controls power supply from the motor drive circuit 36 to the motor 24according to the residing tightening mode and the set torque thereofwith reference to the memory 35, and drives the motor 24 at the initialoutput (V0) (step S302). The reaction receiver 25 thereby rotates in thereverse direction to the tightening direction of the socket and contactsanother fastening member or the like, and the fastening member startsbeing tightened by the socket.

The initial output (V0) is set to satisfy the following relationship,where VB is the minimum starting output of the motor 24: initial outputof normal tightening mode>initial output of hard tightening mode>initialoutput of checking tightening mode≧VB. More favorable checkingtightening can be performed when the initial output of the checkingtightening mode coincides with or most nearly approximates the minimumstarting output (VB).

When the motor 24 starts driving, the torque detector 50 detects thetorque acting on the socket, and transmits the detected torque to thecontrol means 32 as the measured torque. The motor is driven at theinitial output (V0) until the measured torque reaches the prescribedcontrol start torque (VF) corresponding to each tightening mode (No atstep S303; range indicated by circled number 1 in FIGS. 7 to 9). Whenthe measured torque reaches the prescribed control start torque (VF)(YES at step S303; P in FIGS. 7 to 9), motor feedback control is started(step S304; range indicated by circled number 2 in FIGS. 7 to 9). Notethat prescribed torque (VF) can be set in correspondence with thetightening mode. The control start torque (VF) can be set respectivelyin the first tightening process (first control start torque) and thesecond tightening process (second control start torque), in which case:first control start torque (VF)≧second control start torque (VF).Desirably, the following relationship is satisfied: control start torque(VF) of normal tightening mode≧control start torque (VF) of hardtightening mode>control start torque (VF) of checking tightening mode.For example, in FIGS. 7 to 9, the control start torque of the normaltightening mode is 0.7 times the set torque T (VF=T×0.7), the controlstart torque of the hard tightening mode is also 0.7 times the settorque T (VF=T×0.7), and the control start torque of the checkingtightening mode is VF=50 N·m (<T×0.5).

In the motor feedback control (step S304), as shown in FIGS. 7 to 9, inthe case where the rate of increase of measured torque is greater than apredetermined value, based on the measured torque from the torquedetector 50 (Yes in step S305), the control unit 33 performs control toreduce the power supply from the motor drive circuit 36 to the motor 24(step S306), and if the rate of increase of measured torque is less thanor equal to the predetermined value (No in step S305), the processingproceeds to the following step S307.

As shown in FIGS. 7 to 9, conversely, in the case where the rate ofincrease of measured torque from the torque detector 50 is less than apredetermined value (Yes in step S307), the control unit 33 performscontrol to increase the power supply from the motor drive circuit 36 tothe motor 24 (step S308), and if the rate of increase of measured torqueis the predetermined value or greater (No in step S307), the processingproceeds to the following step S309.

The feedback control (steps S305 to S308) is executed until the measuredtorque from the torque detector 50 reaches the set torque T set incorrespondence with each of the tightening modes (No in step S309). Whenmeasured torque reaches the set torque T (Yes in step S309), the controlunit 33 blocks the power supply from the motor drive circuit 36 to themotor 24, and stop the output of the motor 24 (step S310; circled number3 in FIGS. 7 to 9).

A graph showing the change in tightening torque in the tightening flowcorresponding to each tightening mode, and a graph showing the change inoutput of the motor 24 are respectively shown as A and B in FIGS. 7 to9.

Referring to FIGS. 7 to 9, it can be seen that the measured torqueincreases approximately linearly in each of the tightening modes due tothe initial output (V0) being applied, and then when the first controlstart torque or the second control start torque (VF) corresponding tothe tightening mode is reached, the measured torque increases in aphased manner through repeated increases and decreases in torque, andapproaches the set torque T.

Because the motor 24 has a large initial output in the normal tighteningmode and the hard tightening mode serving as the first tighteningprocess, tightening can be performed in a short time, although at therisk of the tightening torque overshooting. In this case, the fasteningmember would be tightened to an even greater tightening torque iftightening in the normal tightening mode or the hard tightening modewere performed in the second tightening process which is for checkingthe tightening torque.

In the present invention, overshooting is unlikely to occur, because thetightening torque is checked in the checking tightening mode of thesecond tightening process in which the initial output (V0) of the motor24 is less than in either the normal tightening mode or the hardtightening mode. Accordingly, it can be accurately confirmed that thefastening member is tightened to the set tightening torque or greater.

That is, when the second tightening process is implemented on afastening member that was tightened to less than the set torque in thefirst tightening process, the tightening torque can be increased to theset torque. On the other hand, when the second tightening process isimplemented on a fastening member that was tightened to the set torqueor greater in the first tightening process, it can be confirmed that thefastening member is tightened to the set torque or greater, withoutfurther increasing or loosening the tightening torque.

Being able to check that tightening has been performed to the set torqueor greater in the second tightening process, without loosening thefastening member, is highly effective when applied to the tightening ofwheel nuts, which was conventionally performed by loosening andretightening the wheel nuts.

The foregoing description is intended to illustrate the presentinvention, and should not be construed as limiting the invention definedin the claims or as restricting the scope of the invention. Also, theconfiguration of each element of the invention is not limited to theforegoing examples, and various modifications can be made within thetechnical scope of the claims.

For example, the first tightening process and the second tighteningprocess can also be executed continuously on each fastening member, orthe first tightening process may firstly be executed on a plurality offastening members, and the second tightening process may then beexecuted collectively on these fastening members. Also, a configurationmay be adopted in which only the second tightening process is executedon a fastening member tightened by another tightening device.

WORKING EXAMPLES Example 1

Tightening of a fastening target with respect to which the torqueincrement from 10% to 100% of the target torque is equivalent to anangular displacement of 27 degrees or less was performed. In thetightening, a F10T high-tensile hexagon bolt (JIS B 1186) having an M45nominal diameter and a length of 130 mm was used as a fastening memberon a steel plate having a thickness of 51 mm.

The set torque was T=600 N·m, and the normal tightening mode and thehard tightening mode were each implemented from an 10 N·m seated stateas the first tightening process. The results are shown in FIG. 10.

Referring to FIG. 10, the tightening torque in the normal tighteningmode greatly overshoots more than the hard tightening mode. Thisindicates that the hard tightening mode is suitable for the firsttightening process on a fastening target with respect to which thetorque increment from 10% to 100% of the target torque is equivalent toan angular displacement of 27 degrees or less.

Next, the second tightening process was implemented after tightening theabovementioned fastening target to 600 N·m in the first tighteningprocess. The checking tightening mode and the hard tightening mode forcomparison were implemented as the second tightening process. Theresults are shown in FIG. 10.

Referring to FIG. 10, it is evident that tightening can be performed toa more accurate tightening torque in the checking tightening modecompared with the hard tightening mode, at a smaller initial output ofthe motor 24.

From the above, it is evident that in tightening a fastening target withrespect to which the torque increment from 10% to 100% of the targettorque is equivalent to an angular displacement of 27 degrees or less,it is favorable to employ a combination of the hard tightening mode asthe first tightening process and the checking tightening mode as thesecond tightening process.

Example 2

Tightening of a fastening target with respect to which the torqueincrement from 10% to 100% of the target torque is equivalent to anangular displacement of over 27 degrees was performed. In thetightening, a F10T high-tensile hexagon bolt (JIS B 1186) having an M24nominal diameter and a length of 90 mm was used as a fastening member ona steel plate having a thickness of 40 mm.

The set torque was T=600 N·m, and the normal tightening mode and thehard tightening mode were each implemented from an 10 N·m seated stateas the first tightening process. The results are shown in FIG. 11.

Referring to FIG. 11, the tightening torque in the normal tighteningmode greatly overshoots more than the hard tightening mode. However, theamount of overshoot amount is small compared with the Example 1.Accordingly, it is evident that the normal tightening mode in whichtightening can be performed in a short time is suitable for the firsttightening process on a fastening target with respect to which thetorque increment from 10% to 100% of the target torque is equivalent toan angular displacement of over 27 degrees.

Next, the second tightening process was implemented after tightening theabovementioned fastening target to 600 N·m in the first tighteningprocess. The checking tightening mode and the hard tightening mode forcomparison were implemented as the second tightening process. Theresults are shown in FIG. 11.

Referring to FIG. 11, it is evident that tightening can be performed toa more accurate tightening torque in the checking tightening modecompared with the hard tightening mode, at a smaller output of the motor24.

From the above, it is evident that in tightening a fastening target withrespect to which the torque increment from 10% to 100% of the targettorque is equivalent to an angular displacement of over 27 degrees, itis favorable to employ a combination of the normal tightening mode asthe first tightening process and the checking tightening mode as thesecond tightening process.

What is claimed is:
 1. A tightening device comprising: a motor; a motordrive circuit that drives the motor; a drive shaft that is rotated bythe motor, has a socket mounted on a tip thereof, and is configured totighten a fastening member; a torque detector that detects a tighteningtorque that acts on the socket; and a control unit that controls themotor drive circuit based on a set torque set in advance and a measuredtorque measured by the torque detector, wherein the control unitexecutes a first tightening process of controlling the motor drivecircuit, adjusting an output of the motor after the measured torque thatis measured by the torque detector has reached a preset first controlstart torque, such that the measured torque reaches a preset first settorque in a phased manner through repeated increases and decreases intorque, and blocking power supply to the motor when the measured torquereaches the first set torque, and then executes a second tighteningprocess of controlling the motor drive circuit to drive the motor at aninitial output that is less than in the first tightening process,adjusting the output of the motor after the measured torque that ismeasured by the torque detector has reached a preset second controlstart torque, such that the measured torque reaches a preset second settorque in a phased manner through repeated increases and decreases intorque while maintaining at least the initial output, and blocking powersupply to the motor when the measured torque reaches the second settorque.
 2. The tightening device according to claim 1, wherein thesecond control start torque is less than the first control start torque.3. The tightening device according to claim 2, wherein the torquedetector is mounted to the drive shaft, and the torque detector and thecontrol unit perform signal transmission and reception by wirelesscommunication.
 4. The tightening device according to claim 1, whereinthe torque detector is mounted to the drive shaft, and the torquedetector and the control unit perform signal transmission and receptionby wireless communication.
 5. A method of controlling a tighteningdevice that includes a motor, a motor drive circuit that drives themotor, a drive shaft that is rotated by the motor, has a socket mountedon a tip thereof, and is configured to tighten a fastening member, and atorque detector that detects a tightening torque that acts on thesocket, the method comprising: a first tightening process of controllingthe motor drive circuit, adjusting an output of the motor after themeasured torque that is measured by the torque detector has reached apreset first control start torque, such that the measured torque reachesa preset first set torque in a phased manner through repeated increasesand decreases in torque, and blocking power supply to the motor when themeasured torque reaches the first set torque; and a second tighteningprocess of controlling the motor drive circuit to drive the motor at aninitial output that is less than in the first tightening process,adjusting the output of the motor after the measured torque that ismeasured by the torque detector has reached a preset second controlstart torque, such that the measured torque reaches a preset second settorque in a phased manner through repeated increases and decreases intorque while maintaining at least the initial output, and blocking powersupply to the motor when the measured torque reaches the second settorque.
 6. The method of controlling a tightening device according toclaim 5, wherein the second control start torque is less than the firstcontrol start torque.
 7. The method of controlling a tightening deviceaccording to claim 6, wherein the first tightening process is executedon a plurality of the fastening members, and then the second tighteningprocess is executed on the plurality of fastening members.
 8. The methodof controlling a tightening device according to claim 5, wherein thefirst tightening process is executed on a plurality of the fasteningmembers, and then the second tightening process is executed on theplurality of fastening members.